The Source of Time-Correlated Photons at 1.064 μm and its Applications

Abstract

Abstract. The source of time-correlated photon-pairs at 1064 nm is described. The source consists of the spontaneous parametric down-conversion (SPDC) generator, pumped by cw laser operating at 532 nm, and the measuring and control appliances. One of the main parts of the electronic systems is the "time-to-digital converter" which is designed and built by our group. The system allows to create and detect correlation of photon pairs with resolution better than 1 ns. We adduce the results of a quantum key distribution through open air. The key length was about 5000 bits and the accuracy ~0.1%. Keywords: quantum optics, spontaneous parametric down-conversionThe SPDC sources of correlated and entangled photons have taken its rightful place in modern quantum optical technologies [1,2]. In present work we report the time-correlated source of photons at 1064 nm and its applications on quantum key distribution via a novel time-algorithm with low error rate. The usage of this wavelength is motivated by potential possibility of applications of such sources as cryptographic sources implemented in existing fiber-based Internet connections with the future YAG:Nd 3+ point-to-point re-transmitters. For the same goal we use the quantum key distribution algorithm based on time-correlations. It should be noted that sources at 1064 nm previously were not widely used due to low quantum efficiency of existing avalanche-photodiodes. But now appropriate detectors for this spectral region have been invented and we may change our mind about this spectral region. Our source is based on the single-crystal SPDC scheme using a BBO crystal. The pump (0-300 mW) was the second harmonic of cw YAG:Nd 3+ diode-pumped laser. It has coherence length of ~ 3 mm. The SPDC crystal is the 3-mm length type-I cut (e-oo) BBO crystal. We use ID Quantique id400 SERIES avalanche photodiode having high quantum efficiency at 1064 nm, the multichannel time-to-digital converter IDQ's id800-TDC and the self-designed, developed as a part of the import substitution programm, time-to-digital converter "TDC-6" having the characteristics shown below: